Chapters 21-24

1. Chapters 21-24 KD-7 Thermodynamics

2. Thermal Energy • Thermal energy-The internal kinetic and potential energy of molecules

3. Heat vs Temperature • Heat-Thermal energy that flows from 1 substance to another • Only flows from high to lower temps. • Symbol: Q • Measured in Joules or calories

4. Heat • Objects exchange heat until they reach equilibrium (same temp.)

5. Heat vs Temperature • Temperature-A quantity proportional to the average kinetic energy of molecules • NOT energy • Symbol: T • Measured in °C, °F, or K

6. Temp. and K.E. • Temp. increases, the K.E. of molecules increase, molecules move faster and expand

7. Important Temps. * There is 100° difference between boiling and freezing on BOTH Celsius and Kelvin, so when we deal with changes of temp. doesn’t matter if we use °C or K

9. To Convert: • K = °C + 273 °C = 5/9 (°F-32) F = (9/5 °C) + 32 * To convert between Fahrenheit and Kelvin, you must 1st convert to Celsius

10. Example: • If the temperature is 75 °F outside, what is the temp. in Kelvin? °C = 5/9 (°F-32) °C = 5/9 (75°-32) °C = 24˚ K = °C + 273 K = 24° + 273 K = 297

11. Specific Heat • Specific Heat-The thermal energy needed to change the temp. of 1 kg of a substance by 1 K (or 1 °C) • Heat added to raise a temp. or taken away to lower a temp. • Symbol: c • Measures in J/kg K

12. Specific Heat of Common Substances • Pg. 46 in workbook

13. Heating/Cooling Curve

14. Change Temperature • Amount of heat needed to change temp. use: • Q = m c ∆T • Q = heat (J) • m = mass (kg) • c = specific heat (J/kg K) • ∆T = change in temp. (K or C)

15. Change State • Amount of heat needed to change state use (materials DO NOT change temperature when they change states): • Q = m Hf or Q = m Hv • m = mass (kg) • Hf = heat of fusion (J/kg) • Hv = heat of vaporization (J/kg)

16. Change State

17. Fusion vs Vaporization • Heat of fusion- Amount of thermal energy needed to change 1 kg of a substance from a solid to a liquid or vice versa • For water: 3.34 X 105 J/kg

18. Fusion vs. Vaporization • Heat of vaporization- Amount of thermal energy needed to change 1 kg of a liquid to a gas (vapor) or vice versa • For water: 2.26 X 106 J/kg

19. Energy change in a single substance • How much energy is removed from 0.25 kg of steam at 150˚C when it is changed to water at 50˚C? Energy to change steam to water Q = m hv Energy to cool steam Q = m c Δ T Energy to cool water Q = m c Δ T .25(2020)(50) .25(2,260,000) .25(4180)(50)